title: Overlapping activity periods in early visual cortex and posterior intraparietal area in conscious visual shape perception: a TMS study.
abstract: Parietal cortex is often activated in brain imaging studies on conscious visual processing, but its causal role and timing in conscious and nonconscious perception are poorly understood. We studied the role of posterior intraparietal sulcus (IPS) and early visual areas (V1/V2) in conscious and nonconscious vision by interfering with their functioning with MRI-guided transcranial magnetic stimulation (TMS). The observers made binary forced-choice decisions concerning the shape or color of the metacontrast masked targets and rated the quality of their conscious perception. TMS was applied 30, 60, 90, or 120ms after stimulus-onset. In the shape discrimination task, TMS of V1/V2 impaired conscious perception at 60, 90, and 120ms and nonconscious perception at 90ms. TMS of IPS impaired only conscious shape perception, also around 90ms. Conscious color perception was facilitated or suppressed depending on the strength of the TMS-induced electric field in V1/V2 at 90ms. The results suggest that simultaneous activity in V1/V2 and IPS around 90ms is necessary for visual awareness of shape but not for nonconscious perception. The overlapping activity periods of IPS and V1/V2 may reflect recurrent interaction between parietal cortex and V1 in conscious shape perception.
authors.affiliation: Department of Psychology, University of Turku, FI-20014 Turun yliopisto, Finland; Centre for Cognitive Neuroscience, University of Turku, FI-20014 Turun yliopisto, Finland. Electronic address: mika.koivisto@utu.fi.
authors.forename: Mika
authors.initials: M
authors.lastname: Koivisto
authors.forename: Mikko
authors.initials: M
authors.lastname: Lähteenmäki
authors.forename: Valtteri
authors.initials: V
authors.lastname: Kaasinen
authors.forename: Riitta
authors.initials: R
authors.lastname: Parkkola
authors.forename: Henry
authors.initials: H
authors.lastname: Railo
mesh_terms: D000328:Adult; D001931:Brain Mapping; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010296:Parietal Lobe / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
keywords: Consciousness; Parietal cortex; TMS; V1